Typically, organic hazardous waste streams are incinerated at approved Hazardous Waste Facilities. When the waste streams comprise primarily water and the BTU content falls to less than 5,000 BTU per pound of waste, alternative treatment technologies become economically viable.
Systems are known for processing hazardous wastes to remove organic pollutants therefrom. Examples of such systems are described, respectively, in U.S. Pat. No. 4,349,415 and U.S. Pat. No. 4,375,387. Organic extraction such as described in these patents uses carbon dioxide flowing upwardly in a column countercurrent to a stream of liquid hazardous waste, as a solvent to strip organics from the waste matrix. At or near its critical point the carbon dioxide behaves like a liquid organic solvent in that it dissolves organic substances in the waste stream, and it behaves like a gas in that its extraction rate is higher than the separation that might be obtained by other means. The organics laden carbon dioxide or extract is removed from the top of the column, while "clean" water is drawn off at the bottom. The organics laden extract is transported to a separator wherein the temperature and pressure are lowered. The organics separate from the carbon dioxide solvent and are recovered in a concentrated form while the carbon dioxide solvent is recycled to the extraction column.
A hazardous waste matrix typically contains heavy metals, along with a variety of organics such as ketones, alcohols, acetates, and aromatic and aliphatic hydrocarbons. Critical fluid extraction as described in the aforesaid patents efficaciously removes organics in aqueous based hazardous wastes, however, the "clean" water drawn off after extraction, is likely to contain toxic heavy metal components.
Processes are known for removing heavy metals from waste water streams. U.S. Pat. No. 4,166,032 describes a system in which heavy metals are separated from the waste water stream by contacting the waste water with a fibrous metal base cellulose xanthate substrate. After the heavy metals are chemisorbed onto the adsorbent cellulose xanthate, the substrate must be separated from the waste water to permit stripping of the heavy metals therefrom. The cellulose xanthate may be removed from the waste water by sedimentation, centrifugation or filtration. Alternatively, a porous bed of cellulose xanthate may be established in a flowthrough contacting reactor.
U.S. Pat. No. 4,342,650 describes a method for converting substantially untreated sludge into useful substances. The treatment involves a chelating step in which heavy metals are removed from suspension and recovered as a recyclable concentrate. The '650 patent describes a chelation process resulting from preliminary steps of disintegration and enzyme hydrolysis which produces a low molecular weight slurry wherein the metal ion content is readily accessible and upon which chelation is effected.
The processes and apparatus known in the art do not concurrently process organics and heavy metals. A process such as described in the '415 and '387 patents only removes organics from the hazardous waste stream. The '032 patent requires the introduction, removal and further processing of cellulose xanthate adsorbent in the contact removal of only heavy metals in a waste stream. The '650 patent requires significant and costly disintegration and enzyme hydrolysis preprocessing in the chelation process which removes only heavy metals from waste slurry.